This invention relates to a flash lamp for underwater photography provided with a so-called target light (to be defined more precisely below), as well as methods and devices for controlling the emission of light from such a target light.
For underwater photography, divers have been carrying along a single-lens reflex camera inside a water-proof housing together with a group of exchange lenses, but a flash lamp is nearly indispensable in underwater photography both because red light is more easily absorbed by water to cause a color imbalance and because there is usually not enough natural light available. As shown in FIG. 1, an underwater flash lamp 90 is usually attached to a camera 91 by means of a flexible arm 92 and is positioned away from the camera 91. One of the reasons for this is that the axis of emitted light from the flash lamp 90 must be displaced (both in terms of position and angle) from the optical axis of the camera 91 because there are usually many small objects such as plankton and grains of same floating inside the water around the underwater photographer. If the flash lamp 90 were set near the camera 91, its light would be strongly reflected by these small objects in front of the target object intended to be photographed and the resulting picture would look like that of a snow scene. Another reason is that underwater photography depends nearly entirely on the light from the flash lamp and hence the position and orientation of the flash lamp should be freely changeable, depending on the desired light condition as well as that of the target object to be photographed.
In underwater photography, the position and orientation of the flash lamp 90 at the end of the flexible arm 92 are adjusted after each exposure in order to get ready for the next opportunity. At the same time, the photographer must check whether the flash lamp 90 is indeed pointing in the direction of the target object to be photographed. Since the visual sense of distance is different in the underwater condition from that in the above-water condition, it is a troublesome work to adjust and check the direction of the optical axis of an underwater flash lamp.
Experienced underwater photographers have learned to attach a penlight 94, as shown in FIG. 1, in order to make this work somewhat easier. Since the penlight 94 is preliminarily attached to the flash lamp 90 such that their optical axes coincide approximately, the underwater photographer can predict the reach of the optical axis of the flash lamp 90 by switching on the penlight 94. This method of attaching a penlight, however, has the following problems:
(1) With the penlight attached, the underwater camera system as a whole becomes bulkier and heavier;
(2) The flux of light emitted from the penlight tends to expand and is likely to be sensed by the fish, which will react and swim away;
(3) Since the flux of light emitted from the penlight expands, it becomes weak by the time it reaches the neighborhood of the target object to be photographed and its direction cannot be ascertained easily by the photographer wearing a goggle;
(4) The penlight requires a bulb with a large output power so as to be effective in the underwater environment and this adversely affects the useful lifetime of the batteries;
(5) Since the batteries for the penlight and for the flash lamp have different lifetimes, it is troublesome to dependably manage them of both; and
(6) It is troublesome to control its operation because it must be switched off before the camera is clicked so as to prevent the light from the penlight from entering the camera.
Although underwater flash lamps incorporating a small light source inside are coming to be available, they can merely serve to simplify the management of batteries somewhat and the problems listed above are mostly unsolved.
Since the underwater photographer usually remains in one position and waits for a right moment to click the shutter while looking into the finder through the goggle, it is desirable to be able to ascertain the condition of the flash lamp without changing the body position and while continuing to look through the finder. In general, the condition of the camera of an underwater photography system (say, a single-lens reflex camera) can be ascertained by means of a display marker which is made visible inside its finder. Since the condition of the flash lamp cannot generally be ascertained merely by looking into the finder, the photographer will have to change the body position, even if temporarily, in order to turn around the system as a whole for checking the display of an LED, for example, on the side surface of the flash lamp for displaying the charge condition, etc. There is usually a current at the site of underwater photography, and the ground condition may not be convenient for the photographer to stand up comfortably or to keep the body in balance. Thus, a heavy labor is involved in moving around the equipment and changing the body position, and an extreme care must be taken.
When a digital cameral placed inside a waterproof housing is used for underwater photography, a flash lamp is sometimes attached to the exterior of the housing because such a housing is likely to interfere with the light from an internally provided flash lamp and the amount of effective light may be thereby diminished. In such a case, a light source, not the flash lamp itself, is sometimes used for assisting the user in focussing the camera because a digital camera is sometime more difficult to focus that a single-lens reflex camera. Such a light source may also serve the purpose of allowing the user to ascertain the position of the target object to be photographed or of illuminating the target object to be photographed for making its image on a liquid crystal display device brighter. Throughout herein, such a light source, not a flash lamp, provided for these and other purposes are referred to, in a broad sense of the expression, as a target light.
FIG. 2 shows an example of timing chart for the control of light emission from such a light source (the target light) for a flash lamp adapted to emit flash light preliminarily first and then for the second time as the main emission. When the shutter button is clicked, the flash lamp undergoes a preliminarily light emission before the shutter is opened and the reflected light is instantaneously measured for determining the quantity of light to be projected by the main emission. In this example, the target light remains turned on until the shutter is opened and is switched off in synchronism with the signal through the so-called X-contact (that is, the point where a signal for opening the shutter is transmitted), that is, simultaneously with the starting of the main emission of the flash lamp. If the flash lamp is of the type which undergoes only the main light emission (or the so-called xe2x80x9cauto-stroboscopicxe2x80x9d or xe2x80x9cflashmatic-typexe2x80x9d), there is no preliminary emission and the main emission is adapted to be carried out with a suitable exposure. In this case, too, the target light is switched off in synchronism with a signal through the X-contact.
This prior art method of controlling the timing for switching off a target light has the following problem. Since the shutter for a digital camera operates more slowly than that of an ordinary single-lens reflex camera (indicated by the slope of the curve for the shutter position in FIG. 2), digital cameras are designed, in view of the fluctuations in the time required for the shutter to open completely, such that the X-contact will be switched on slightly after the shutter is completely opened. As a result, it sometimes happens that the target light stays switched on even after the shutter has begun to open until the main emission from the flash lamp is started (shown as time period ta in FIG. 2), allowing its light to enter the camera through its lens and adversely affecting the quality of the picture taken.
It is an object of this invention to provide an improved flash lamp for underwater photography with which the problem of setting its optical axis and checking its conditions can be obviated such that the photographer""s work in setting and checking the optical axis of the flash lamp, for example, becomes much simpler and underwater photography becomes much easier.
It is another object of the invention to provide a control method and device for controlling the target light for a camera for underwater photography such as a digital camera in a waterproof housing such that light therefrom can be effectively prevented from entering the camera before it is switched off.
A flash lamp embodying this invention, with which the first of the objects of this invention described above can be achieved, may be characterized generally as comprising not only a discharge tube of a known kind for emitting flash light but also a target light such as a laser diode or a well-focussed LED and a control means for automatically switching off the target light approximately simultaneously as the shutter of the camera attached to the flash lamp is opened. Merits of a flash lamp provided with such a target light, as ascertained experimentally by the present inventors, include the following:
(1) A beam from such a target light remains well focussed even in water and can reach several tens of meters without becoming dispersed;
(2) Since a beam of light from such a well-focussed source can travel a long distance without dispersing, the user can clearly ascertain the direction of its propagation;
(3) Since a beam of light from such a target light is narrowly focussed, it is usually ignored by the fish to be photographed;
(4) A narrowly focussed beam from such a target light is not sensed by the fish being aimed at even if it is received by its eye;
(5) A narrowly focussed beam from such a target light is not dispersed much inside water and remains as a spot light even at a long distance and hence can be easily observed by the user even through a goggle; and
(6) A narrowly focussed beam from such a target light is not dispersed much inside water and remains a strongly focussed spot light even in the neighborhood of a distant object to be photographed and hence can be effective for the focussing of the camera, whether it is by an automatic focussing mechanism or even by manual focussing by the user.
With a flash lamp using a conventional penlight as a target light, it seldom is a problem if the target light remains on when the shutter of the camera is opened because brightness of the flash light is much greater than that of the penlight. With a flash lamp embodying this invention with a laser diode or a focussed LED serving as the target light, experiments by the inventors showed that a spot may appear on the resulting picture if the target light remains switched on when the shutter is opened for the exposure. Thus, flash lamps embodying this invention must include means for automatically switching off the target light approximately simultaneously as the shutter is opened. As will be explained below, however, this synchronism between the time to open the shutter and the time to turn off the target light need not be exact, and this gives a certain degree of freedom in the circuit design within this limiting requirement.
It is preferable to use a highly convergent light source such as a laser diode as the target light because it can form a spot light sufficiently small compared to the target object to be photographed such as a fish. Experiments by the inventors showed that it was possible to point the target light from a flash lamp embodying this invention on a fish to be photographed without alarming it. Ordinary laser light pointers for use in a lecture hall are designed such that the pointed spot be visible by many persons attending the lecture and hence its diameter is usually designed to be about 10 mm. For the purpose of the present invention, the spot light on the target object to be photographed is only for the user to see. The diameter of the spot light at the position of the target object to be photographed is therefore designed to be no greater than several mm.
Eyes of a fish are usually protruding from the head such that a wider angle of vision is had. By contrast, light from a laser diode is very narrow and is believed not easily recognized by a fish. Tests were carried out by the present inventors by intentionally aiming the beam from a laser diode on the fish""s eyes by moving it around to cover an extended area to stimulate the fish. Tests were also carried out by changing color of the emitted light. As a result of such series of tests, it was ascertained that the size of the area of the spot light is an important factor.
A flash lamp embodying this invention is further characterized as comprising one or more of the following mechanisms for switching on the target light:
(1) a mechanism for switching on the target light approximately simultaneously as when the flash lamp has been charged;
(2) a mechanism for switching on the target light when the shutter button of the camera for opening its shutter has been pushed in by the user to a half-way position and a signal indicative of this condition (referred to as the xe2x80x9chalf-pushed-in signalxe2x80x9d or the xe2x80x9cready signalxe2x80x9d) has been thereby generated and is received by the mechanism; and
(3) a mechanism for switching on the target light by a timer, or in response to a timer signal generated by a timer and received by the mechanism.
With one or more of such mechanisms provided, the user has only to switch on the power switch on the flash lamp. Since the target light is turned on semi-automatically thereafter when any of the conditions described above comes to be satisfied, the user has only to wait, for example, until a colored spot light becomes visible through the finder of the camera. In other words, the user is no longer required to change the body position to learn the condition in which the flash lamp is (that is, whether it has been charged and where it is pointed) and can concentrate on the next picture to be taken. The timer, referred to above, need not be of the ordinary kind for measuring time but may be any of various circuit units having a timer-like function such as a so-called one-shot multi-vibrator circuit which remains in a switched-on condition for several to several tens of seconds when a trigger signal is received by the gate switch.
A flash lamp according to a preferred embodiment of the invention may be further adapted to be operable in an energy-saving mode, being provided with one or both of the following mechanisms:
(1) an energy-saving mechanism for switching on the target light after the flash lamp has been charged and the half-pushed-in signal has been received; and
(2) an energy-saving mechanism for switching on the target light after the flash lamp has been charged and when a timer signal has been received from a timer.
The water temperature is usually low at the site of underwater photography and the heat generated by the electrical circuits and the light-emitting components is quickly conducted away. Under such a low-temperature condition, the dry cell batteries cannot function as effectively and power tends to be wasted quickly. An energy-saving mode of operation, therefore, is an important feature of this invention. The conditions related to the energy-saving mechanisms mentioned above are not substantially different from those for ordinary systems for above-ground use. Thus, users will not find them unfamiliar and will be able to become used to them quickly.
Signals exchanged between the flash lamp and the camera to which it is connected may be at least in part optical signals transmitted through an optical signal cable. Use of an optical signal cable to connect the flash lamp with the camera is advantageous because the connecting parts are not damaged by the invasion of water.
A method embodying this invention, with which the second of the aforementioned objects can be accomplished, may be characterized, if the flash lamp is of the kind adapted to undergo both preliminary flash light emission and main flash light emission, as comprising the step of darkening (including switching off) the target light to a darkened condition (including an totally extinguished condition) by using the preliminary flash light emission as a trigger before the shutter of the camera begins to open. The target light is then kept in the darkened condition at least until the shutter is closed. If the flash lamp is of the kind adapted to undergo only the main flash light emission without any preliminary flash light emission, the so-called ready signal which may be outputted when the shutter button is pressed to a half-way position, is used as the trigger.
A device embodying this invention, with which the second of the aforementioned objects can be accomplished, may be characterized, if the flash lamp is of the kind adapted to undergo both preliminary flash light emission and main flash light emission, as comprising control means for darkening the target light to a darkened condition by using the preliminary flash emission as a trigger before the shutter begins to open. The control means will further serve to keep the target light in the darkened condition at least until the shutter is closed. If the flash lamp is of the kind adapted to undergo only the main flash light emission without any preliminary flash light emission, detecting means is provided for detecting a so-called ready signal which may be outputted when the shutter button of the camera is pressed to a half-way position and outputting a detection signal when the ready signal is detected and a control means serves to darken the target light when this detection signal is received.